1. Field of the Invention
The present invention relates to a charged particle beam writing apparatus and a charged particle beam writing method and, for example, relates to a technique to determine the dose of an electron beam to improve uniformity in line width in electron beam writing.
2. Related Art
A lithography technique, which leads development of micropatterning of a semiconductor device, is a very important process for exclusively generating a pattern in semiconductor manufacturing processes. In recent years, with an increase in integration density of an LSI, a circuit line width required for semiconductor devices is getting smaller year by year. In order to form a desired circuit pattern on such semiconductor devices, a high-precision original pattern (also called a reticle or a mask) is necessary. In this case, an electron beam writing technique has an essentially excellent resolution, and is used in production of high-precision original patterns.
FIG. 20 is a conceptual diagram for describing an operation of a variable-shaped electron beam writing apparatus.
The variable-shaped electron beam (EB) writing apparatus operates as described below. An oblong, for example, rectangular opening 411 to shape an electron beam 330 is formed in a first aperture plate 410. A variable-shaped opening 421 to shape the electron beam 330 having passed through the opening 411 of the first aperture plate 410 into a desired oblong shape is formed in a second aperture plate 420. The electron beam 330 irradiated from a charged particle source 430 and having passed through the opening 411 of the first aperture plate 410 is deflected by a deflector, passes through a part of the variable-shaped opening 421 of the second aperture plate 420, and is shone on a target object 340 placed on a stage continuously moving in one predetermined direction (for example, an X direction). That is, an oblong shape which can pass through both the opening 411 of the first aperture plate 410 and the variable-shaped opening 421 of the second aperture plate 420 is written in a write region of the target object 340 placed on the stage continuously moving in the X direction. A scheme which causes an electron beam to pass through both the opening 411 of the first aperture plate 410 and the variable-shaped opening 421 of the second aperture plate 420 to form an arbitrary shape is called a variable-shaping scheme (VSB scheme).
In the electron beam writing described above, more precise uniformity in line width in a target object plane, for example, a mask plane is demanded. In such electron beam writing, if a mask coated with a resist is irradiated with an electron beam to write a circuit pattern, a phenomenon called a proximity effect caused by back scattering of the electron beam that passes through the resist layer to reach a layer below the resist layer and then reenters the resist layer occurs. Dimensional fluctuations in which lines are written in dimensions deviating from desired dimensions when lines are written are thereby caused. On the other hand, dimensional fluctuations called a loading effect resulting from the density of circuit patterns are caused also when the development or etching is performed after writing.
The dose of an electron beam is calculated as a product of, for example, a base dose Dbase and a proximity effect-corrected dose Dp(η,U) depending on a proximity effect correction coefficient η to correct the proximity effect and a pattern area density ρ or a proximity effect density U. The proximity effect correction coefficient η that fits the proximity effect correction well is present for each base dose Dbase. Dimensions of a resist image increase with an increasing base dose Dbase.
Thus, a first technique that also corrects dimensional fluctuations caused by the loading effect while maintaining the proximity effect correction by changing the set of the base dose Dbase and the proximity effect correction coefficient η for each position of a substrate is known (see Japanese Patent Application Laid-Open No. 2007-150243, for example). In recent years, the user is required to create set data of a base dose Dbase map and a proximity effect correction coefficient η map for each cause of dimensional fluctuations such as the loading effect and to write using such a plurality of set data on the writing device side. However, the base dose Dbase and the proximity effect correction coefficient η cannot simply be combined and thus, it is difficult to use a plurality of set data for writing on the writing apparatus side.
In doses obtained by the first technique, the same dimensional variation is obtained regardless of the proximity effect density U. That is, a dimensional correction is made such that the proximity effect correction is not shifted. Such a dimensional correction is appropriate for correction of the loading effect caused during etching of a light-shielding film after writing.
On the other hand, a second technique that makes correction by changing the base dose Dbase in accordance with the dimension to be corrected and the dose latitude without changing the proximity effect correction coefficient η is also known. According to the second technique, a different amount of dimensional correction is obtained for each proximity effect density. The technique is appropriate for correction when the embedded dose adjusted by the proximity effect correction deviates from a threshold at the time of developing a resist. Therefore, the second technique is appropriate for correction of the loading effect resulting from non-uniformity of the development threshold caused by irregularities in density of a developing solution.
An error in pattern dimensions caused by the loading effect when a mask is actually produced has the loading effect during development and the loading effect during etching as described above merged therein. That is, both effects may be mixed in the same position. Thus, the correction by one of the above techniques may not be enough. Therefore, a third technique by which the former is corrected by the first technique and the latter by the second technique is discussed. However, it is necessary for the user to separate dimensional errors that actually occur into components for the first technique and components for the second technique to make corrections by the third technique and it is very difficult to do this. Moreover, the above third technique cannot be applied if it becomes necessary to change the proximity effect correction coefficient η used for correction between the loading effect during development and the loading effect during etching.
As described above, the user is required to create set data of a base dose Dbase map and a proximity effect correction coefficient η map for each cause of dimensional fluctuations such as the loading effect and to write using such a plurality of set data on the writing device side. However, there is a problem that even if the plurality of set data is input from the writing device side, it is difficult to write by combining the plurality of set data.
Moreover, both of the above techniques have a problem that it is difficult to make adequate corrections of both of dimensional fluctuations caused by the loading effect during development and dimensional fluctuations caused by the loading effect during etching while correcting the proximity effect.